Organic acid esters of cellulose



Patented Mar. 9, 1954 ORGANIC ACID ESTERS OF CELLULOSE Mark Plunguiam Gillette, N. J., assignor to Celanese Corporation of America,

\ Delaware a corporation of No Drawing. Application May 1, 1951, Serial No. 224,073

Claims. (Cl. 260-229) This invention relates to organic acid esters of cellulose and relates more particularly to an improved process for the production of organic acid esters of cellulose from cellulosic material.

In the production of organic acid esters of cellulose from cellulosic material, it is customary to pretreat the cellulosic material before esterification to increase and make more uniform its reactivity. The pretreated cellulosic material is then esterified with an organic acid anhydride in the presence of relatively large amounts, say from about '7 to 14% by weight on the weight of the cellulosic material, of anesterification catalyst, such as sulfuric acid, and a solvent for the organic acid ester of cellulose, such as a lower aliphatic acid. When the organic acid anhydride is brought into contact with the pretreated cellulosic material in the presence of the relatively large amount of sulfuric acid heretofore employed, the strongly exothermic reaction which takes place tends to cause a rapid rise in the temperature of the reaction mixture. If the temperature of the reaction mixture is permitted to rise unchecked, it will reach a point at which the cellulosic material will be degraded and the organic acid ester of cellulose produced therefrom will not be suitable for commercial application. To control the temperature of the reaction mixture, it is the practice to carry out the esterification in a jacketed vessel'and to pass a cooling medium, such as chilled brine, through the jacket during at least the early stages of the reaction. In addition, it is the practice to cool the organic acid anhydride and lower aliphatic acid that are to be employed for the esterification, generally to a point where the bulk of the lower aliphatic acid is frozen. The refrigeration required to control the temperature of the reaction mixture in the foregoing manner adds appreciably to the cost of manufacturing the organic acid ester of cellulose.

Attempts to eliminate or curtail the amount of cooling required to control the temperature of the reaction mixture by reducing the amount of sulfuric acid present during the esterification have not been successful since, when the amount of sulfuric acid drops to less than about 7% by weight on the weight of the cellulosic material, the reaction mixture tends to solidify or gel unless extremely large quantities of the lower aliphatic acid solvent are present therein. This expedient is uneconomic because of the resultant high dilution of the solutions obtained at the completion of the esterification and the cost of recovering the large quantities of the lower aliphatic acid solvent.

2 It is an important object of this invention to provide a process for the production of organic acid esters of cellulose which will be free from the foregoing and other disadvantages and which will be especially simple and efficient in operation.

A further object of this invention is to provide a process for the production of organic acid esters of cellulose requiring little or no cooling to control the temperature of the reaction mixture.

Another object of this invention is to provide a process for the production of organic acid esters of cellulose in the presence of relatively small amounts of an esteriflcation catalyst in which an aldehyde is added to the cellulosic material before' esteriflcation.

Other objects of this invention will be apparent from the following detailed description and claims.

According to the present invention, it has been discovered that the addition to the cellulosic material before esterification of relatively small quantities of an aldehyde will prevent the solidification or gelling of the reaction mixture when the esterification of the cellulosic material is carried out in the presence of relatively small amounts of sulfuric acid. Among the aldehydes that 'may be employed are, for example, formaldehyde and acetaldehyde, but the best results are obtained by the use of formaldehyde since it is most effective in preventing the solidification or gelling of the reaction mixture. Thus, by adding to the cellulosic material before esterification from about 0.5 to 4 parts by weight of the aldehyde employed for each parts by weight of the cellulosic material, the esteriflcation of said cellulosic material may be readily effected in the presence of between about 0.2 to 5.0 parts by weight of sulfuric acid and from about 600 to 800 parts by weight of the lower aliphatic acid solvent (including the lower aliphatic acid that is formed from the organic acid anhydride before and during the esterification) for each 100 parts by weight of the cellulosic material, and the reaction mixture will show no tendency to solidify or gel. When this small quantity of sulfuric acid is present during the esterification, little or no cooling is required to control the temperature of the reaction mixture. In many cases it may even be necessary to heat the reaction mixture to cause the esterification to proceed to completion, which heating may be effected more easily and at lower cost than the.

cooling hitherto required to prevent an excessive rise in the temperature of the reaction mixture. The aldehyde may be added to the cellulosic 3 material before, during or after the pretreatment of said material, when a pretreatment is employed, but it must, in all cases; be added to the cellulosic material before the addition there to of the organic acid anhydride esterifying agent effectively to prevent the solidification or gelling of the reaction mixture. For example, when the cellulosic material is pretreated in one or more stages with a lower aliphatic acid, as, for example, formic, acetic, propionic, or butyric acid, as well as mixtures thereof, and. if desired. an esterification catalyst, the aldehyde may be incorporated with one of the pretreating solutions, or it may be separately added to the cellulosic material before, after or at any stage of the pretreatment. However, the best results are obtained when the aldehyde is added to the cellulosic material after the pretreatment thereof but before the addition thereto or the organic acid anhydride esterifying agent. The desired amount of aldehyde may be added to the cellulosic material in aqueous solutions, in acetic acid solution,

or in any other desired manner. The addition of the aldehyde to the cellulosic material is advantageously effected at temperatures of between about 20 and 50 C.

Following the pretreatment, the cellulosic material may be esterified in conventional manner with an esterification solution comprising an organic acid anhydride and, if desired, a lower aliphatic acid. Advantageously, however, the organic acid anhydride is added to the cellulosic material in two stages. During the first stage, a sufficient quantity of the organic acid anhydride is added to the cellulosic material to react with all the water present therein. Then, after the rise in temperature caused by the reaction between the organic acid anhydride and the water has subsided, the remainder of the organic acid anhydride is added to the cellulosic material. The esterification of the cellulosic material is then preferably effected at a maximum temperature of between about 30 and 85 C. Depending upon the quantity of sulfuric acid present in the reaction mixture, a slight degree of cooling may be required to keep the temperature of said mixture at the desired level. With the preferred quantities of sulfuric acid specified above, however, it may be necessary to heat the reaction mixture to achieve said temperatures and to cause the esterification to go to completion.

After the esterification of the cellulosic material is complete, th organic acid ester of cellulose may be hydrolyzed or ripened to impart the desired solubility characteristics thereto. When the ripening is to be effected at high temperatures, say above about 65 C., all or a portion of the sulfuric acid catalyst may be neutralized with an alkaline material such as sodium acetate or magnesium acetate before the ripening begins. At lower ripening temperatures, no neutralization of the sulfuric acid catalyst is required. In addition, there is preferably added to the reaction mixture obtained upon completion of the esterification sufficient water to react with all the organic acid anhydride remaining therein plus an excess of between about 100 and 500 parts by weight for each 100 parts by weight of the cellulosic material. Upon completion of the ripening, the cellulosic material isprecipitated, washed, stabilized if necessary, washed again and dried, all in a manner well known in the art.

The process of this invention will now be described specifically in connection with the production of cellulose acetate which is commercially the most important organic acid ester of cellulose at the present time. It is to be understood. however, that it may also be employed for the production of other organic acid esters of oeliulose, such as cellulose acetate propionate and cellulose acetate butyrate, by replacing acetic anhydride with the corresponding organic acid anhydrides.

The following examples are given to illustrate this invention further:

Example I To 100 parts by weight of willowed cotton linters containing 5 parts by weight of water there is added 35 parts by weight of acetic acid and the cotton linters are tumbled for 10 minutes. The cotton linters are then transferred to a jacketed acetylizer equipped with stirring arms and 310 parts by weight of acetic acid and 0.2 part by weight of sulfuric acid are added thereto. The temperature of the mixture is raised with stirring to 33 C., in a period of 10 minutes. There is then added to the mixture 5.4 parts by weight of a 37% (by weight) aqueous formaldehyde solution (2 parts by weight formaldehyde). To the acetylizer are then added 270 parts by weight of acetic anhydride. The temperature is raised to -83 C. quickly by means of hot water in the Jacket and held at this point for 15 minutes to complete the acetylation. Sufficient water is then added to the reaction mixture to convert all the acetic acid anhydride to acetic acid plus an excess of 150 parts by weight. The organic acid ester of cellulose is then ripened. precipitated, washed and dried in conventional manner. sulfuric acid present during the esterification, the reaction mixture shows no tendency to solidify or gel.

Example II To parts by weight of willowed cotton linters containing 5 parts by weight of water there is added 35 parts by weight of acetic acid and the cotton linters are tumbled for 10 minutes. The cotton linters are then transferred to a jacketed acetylizer equipped with stirring arms and 310 parts by weight of acetic acid and 0.5 part by weight of sulfuric acid are added thereto. Stirring is continued at room temperature for 10 minutes. There is then added to the mixture 5.4 parts by weight of a 37% aqueous formaldehyde solution (2 parts by weight formaldehyde). To the acetylizer are then added 270 parts by weight of acetic anhydride. The

temperature is raised to 60 C. quickly by means Example III I To 100 parts by weight of willowed cotton linters containing 5 parts by weight of water there is added 35 parts by weight of acetic acid and the cotton linters are tumbled for 10 minutes. The cotton linters are then transferred Despite the small amount of to a jacketed acetylizer equipped with stirring arms and 310 parts by weight of acetic acid and 2 parts by weight of sulfuric acid are added thereto. Stirring is continued at room tempera: ture for 5 minutes. There is then added to the mixture 2.7 parts by weight of a 37% aqueous formaldehyde solution (1 part by weight formaldehyde). To the acetylizer are then added 270 parts by weight of acetic anhydride. Without either external heating or cooling the temperature of reaction increases to 65 C. in 9 minutes to complete the acetylation. Sufllcient water is then added to the reaction mixture to convert all the acetic anhydride to acetic acid plus an excess of 150 parts by weight. The organic acid ester of cellulose is then ripened, precipitated, washed and dried in conventional manner. Despite the small amount of sulfuric'acid present during the esterification, the reaction mixture shows no tendency to solidify or gel.

Example IV To 100 parts by weight of willowed cotton' linters containing 5 parts by weight of water there is added 35 parts by weight of acetic acid and the cotton linters are tumbled for 10 minutes. The cotton linters are then transferred to a jacketed acetylizer equipped with stirring arms and 310 parts by weight of acetic acid and 0.5 part by weight of sulfuric acid are added thereto. The temperature of the mixture is raised with stirring, in a period of about minutes, to 65 C. by passing the hot water through the acetylizer jacket and the mixture is then immediately cooled to between 45 and 50 C. There is then added to the mixture, with stirring, 2 parts by weight of paraldehyde. To the acetylizer are then added 40 parts by weight of acetic anhydride to react with the water therein and, after the rise in temperature caused by this reaction has subsided, an additional 230 parts by weight of acetic anhydride are added thereto. The temperature of the reaction mixture is then raised to 65 C. by passing hot water through the acetylizer jacket and is held at this point until the esteriflcation is complete, a period of 30 minutes. Sufilcient water is then added to the reaction mixture to convert all the acetic acid anhydride to acetic acid plus an excess of 150 parts by weight. The organic acid ester of cellulose is then ripened, precipitated, washed and dried in conventional manner. Despite the small amount of sulfuric acid present during the esterification, the reaction mixture shows no tendency to solidify or gel.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patent is:

1. In a process for the production of organic acid esters of cellulose from cellulosic material, the steps which comprise adding to the cellulosic material, prior to any esterification thereof, a lower aliphatic aldehyde, and then esterifying the cellulosic material with a lower aliphatic acid anhydride in the presence of between about 0.2 and 5.0 parts byv weight of an esteriflcation catalyst for each 100 parts by weight of the cellulosic material.

2. In a process for the production of organic acid esters of cellulose from cellulosic material, the steps which comprise adding to the cellulosic 6 material, prior to any esteriilcation thereof, a lower aliphatic aldehyde, and then esterifying the cellulosic material with a lower aliphatic acid anhydride in the presence of from about 0.2 to 5 5.0 parts by weight of sulfuric acid for each 100 parts by weight of the cellulosic material.

3. In a process for the production of organic acid esters of cellulose from cellulosic material, the steps which comprise adding to the-cellulosic material, prior to any esterification thereof, a lower aliphatic aldehyde, and then esterifying the cellulosic material with a lower aliphatic acid, anhydride in the presence of between about 0.2 and 5.0 parts by weight of an esteriflcation catalyst for each 100 parts by weight of the cellulosic material and from about 600 to 800 parts by weightof a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

4. In a process for the production of organic acid esters of cellulose from cellulosic material, the steps which comprise adding to the cellulosic material, prior to any esterification thereof, formaldehyde, and then esterifyhKgflthe cellulosic material with a lower aliphatic cid anhydride in the presence of from about 0.2 o 5.0 parts by weight of an esterification catalyst for each 100 parts by weight of the cellulosic material and from about 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

5. In a process for the production of organic acid esters of cellulose from cellulosic material, the steps which comprise adding to the cellulosic material, prior to any esterification thereof, from about 0.5 to 4 parts by weight of a lower alphatic aldehyde for each 100 parts by weight of the cellulosic material, and then esterifying the cellulosic material with a lower aliphatic acid anhydride in the presence of between about 0.2 and 5.0 parts by weight of an esterification catalyst for each 100 parts by weight of the cellulosic material.

6. In a process for the production of organic 43 acid esters of cellulose from cellulosic material,

the steps which comprise adding to the cellulosic material, prior to any esteriflcation thereof, from about 0.5 to 4 parts by weight of formaldehyde for each 100 parts by weight of the cellulosic material, and then esterifying the cellulosic material with a lower aliphatic acid anhydride in the presence of from about 0.2 to 5.0-parts by weight of an esterification catalyst for each 100 parts by weight of the cellulosic material and 0 from about 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

7. In a process for the production of organic acid esters of cellulose from cellulosic material, the steps which comprise adding to the cellulosic material, prior to any esterification thereof, formaldehyde, and then esterifying the cellulosic material with a lower aliphatic acid anhydride in the presence of from about 0.2 to 5.0 parts by weight of sulfuric acid for each 100 parts by weight of the cellulosic material.

8. In a process for the production of organic acid esters of cellulose from cellulosic material, the steps which comprise adding to the cellulosic material, prior to any esterification thereof, formaldehyde, and then esterifying the cellulosic material with a lower aliphatic acid-\a hydride in the presence of from about 0.2 to 5.0 parts by weight of sulfuric acid for each 100 parts by weight of the cellulosic material and from about 7 v 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

9. In a process for the production of organic acid esters of cellulose'from cellulosic material, the steps which comprise adding to the cellulosic material, prior to any esteriilcation thereof, from about 0.5 to 4 parts by weight of formaldehyde for each 100 parts by weight of the cellulosic material, and then esterifying the cellulosic material with a lower aliphatic acid anhydride in the presence of from about 0.2 to 5 parts by weight of sulfuric acid for each 100 parts by weight of the cellulosic material and from about 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

10. In a process for the production of cellulose acetate from cellulosic material, the steps which comprise activating the cellulosic material, adding formaldehyde to the activated cellulosic material, prior to any esterification of said cellulosic materials, and then esterifying the cellulosic material with acetic anhydride in the presence of from about 0.2 to 5 parts by weight of an esterification catalyst for each 100 parts by weight of the cellulosic material and from about 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

11. In a process for the production of cellulose acetate from cellulosic material, the steps which comprise activating the cellulosic material, adding to the activated cellulosic material from about 0.5 to 4 parts by weight of a lower aliphatic aldehyde for each 100 parts by weight of the cellulosic material, and then esterifying the cellulosic material with acetic anhydride in the presence of from about 0.2 to 5 parts by weights of an esteriflcation catalyst for each 100 parts by weight of the cellulosic material and from about 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

12. In a process for the production of cellulose acetate from cellulosic material, the steps which comprise activating the cellulosic material, adding to the activated cellulosic material from about 0.5 to 4 parts by weight of formaldehyde for each 100 parts by weight of the cellulosic material, and then esterifying the cellulosic material with acetic anhydride in the presence of from about 0.2 to 5 parts by weight of sulfuric acid for each 100 parts by weight of the cellulosic material and from about 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material 13. In a process for the production of cellulose acetate from cellulosic material, the steps which comprise activating the cellulosic material, add- 8 to the activated'cellulosic material from about 0.5 to 4 parts by weight of formaldehyde for each 100 parts by weight of the cellulosic material at a temperature of between about 20 and 50 C., and then esterifying the cellulosic material with acetic anhydride in the presence of from about 0.2 to 5 parts by weight of sulfuric acid for each 100 parts by weight of the cellulosic material and from about 600 to 800 parts by weight of a lower aliphatic acidv for each 100 parts by weight of the cellulosic material.

14. In a process for the production of cellulose acetate from cellulosic material, the steps which comprise activating the cellulosic material, adding to the activated cellulosic material from about 0.5 to 4 parts by weight of formaldehyde for each 100 parts by weight of the cellulosic material at a temperature of between about 20 and 50 C., and esterifying the cellulosic material with acetic anhydride at a temperature of between about 40 and 85 C. in the presence of from about 0.2 to 5 parts by weight of sulfuric acid for each 100 parts by weight of the cellulosic material and from about 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

15. In a process for the production of cellulose acetate from cellulosic material, the steps which comprise activating the cellulosic material with a lower aliphatic acid in a plurality of stages, adding to the activated cellulosic material from about 0.5 to 4 parts by weight of formaldehyde for each 100 parts by weight of the cellulosic material at a temperature or between about 20 and 50 C., and then esterifying the cellulosic material with acetic anhydride at a temperature of between about 30 and C. in the presence of from about 0.2 to 5 parts by weight of sulfuric acid for each parts by weight of the cellulosic material and from about 600 to 800 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material.

MARK PLUNGUIAN.

Name Date Zdanovich Feb. 13, 1923 Number 

1. IN A PROCESS FOR THE PRODUCTION OF ORGANIC ACID ESTERS OF CELLULOSE FROM CELLULOSIC MATERIAL THE STEPS WHICH COMPRISE ADDING TO THE CELLULOSIC MATERIAL, PRIOR TO ANY ESTERIFICATION THEREOF, A LOWER ALIPHATIC ALDEHYDE, AND THEN ESTERIFYING THE CELLULOSIC MATERIAL WITH A LOWER ALIPHATIC ACID ANHYDRIDE IN THE PRESENCE OF BETWEEN ABOUT 0.2 AND 5.0 PARTS BY WEIGHT OF AN ESTERIFICATION CATALYST FOR EACH 100 PARTS BY WEIGHT OF THE CELLULOSIC. MATERIAL. 